Issue 12 - October 2013

Photo of Steve Unwin
Direct Detection of Exoplanets: Mission Studies Are Underway
By Steve Unwin
In May 2013, NASA chartered two Science and Technology Definition Teams (STDTs) to develop probe-scale mission concepts for direct detection and spectroscopy of exoplanets. Karl Stapelfeldt's team is studying a mission based on a telescope with an internal coronagraph; Sara Seager's team is looking at blocking out the interfering starlight using an external occulter (starshade) that flies in formation with a telescope. The teams are now well into their studies, and have met in person twice so far, opting to hold meetings at the team leaders’ home institutions -- at GSFC on July 1-2, and at MIT on September 11-12. At the first meeting, the teams were introduced to the Design Team, staffed through the Exoplanet Exploration Program's Study Office and led by Keith Warfield (JPL). The program presented an overview of the task ahead, which culminates in early 2015 with the delivery of Concept Study Reports (one from each team) to NASA HQ. To be fully responsive to the STDT charter, a mission concept must have certain attributes -- most notably a cost target. These reports will become a key part of the Astrophysics Division's presentation to the NRC Committee on Astronomy and Astrophysics, which is chartered to review NASA's progress in implementing the recommendations of the 2010 Astronomy and Astrophysics Decadal Survey. At the meetings so far, the teams have discussed topics in common in joint session. These include the high-level science requirements and related considerations, like the expected state of knowledge in the exoplanet field from ground- and space-based observations prior to the nominal flight date of a probe-scale mission (early 2020s). By then, the next generation of large ground-based telescopes will be coming online (Thirty Meter Telescope, Giant Magellan Telescope, and European Extremely Large Telescope); each is developing high-contrast imaging instruments, though their projected performance is very uncertain at this early stage in their development. Each team has the task of narrowing down possible instrument architectures during fall 2013, with selection in January 2014 of a single concept to develop in detail for the final year of the studies. There was a lively discussion at the first meeting on what constitutes science "musts," which would be used to guide that process. At both meetings so far, the teams split into parallel sessions to work on the specific design and performance issues that feed into the architecture trade. Both teams, assisted by the Design Team, have made rapid progress; the existence of a number of relevant previous concept studies has helped, even though they were developed under different sets of constraints. The teams have already provided the program with a preliminary list of key technologies for their concepts to aid in technology planning. In parallel, the Study Office has been laying the groundwork for developing cost estimates for the two concepts to be selected in January. The charter calls for a Cost Analysis and Technical Evaluation (CATE) to be conducted by an independent contractor. Members of the Aerospace Corporation CATE team met with program staff on September 3 to discuss their process. This was very informative, and will help the STDTs and Design Team to develop good cost estimates by allowing enough time for interaction with the CATE team to understand the details of each concept. There will be status updates at ExoPAG-8 ( in Denver October 5-6; at ExoPAG-9 [no link yet], at the Washington, DC, AAS meeting (January 4-5), and also at an evening session there. Web pages devoted to the STDTs on the ExEP website are at, where you can find the team membership lists and the charter that governs their work. As the studies progress, we will add updates and news. Public versions of the final reports should be available in mid-2015.